The present invention relates generally to estimation of a signal-to-interference ratio in a wireless communication receiver.
In a wireless communication system, the receiver typically calculates the signal-to-interference ratio (SIR) associated with a receive signal and use the calculated SIR to adapt the transmission parameters to current channel conditions. For example, the calculated SIR may be used to control the mobile station transmit power, data transmission rate, and modulation and coding scheme. Additionally, the calculated SIR may be used to generate a channel quality indicator (CQI) for scheduling purposes.
Conventionally, estimates of the SIR are derived from pilot symbols. Pilot symbols are known symbols that are transmitted over the communication channel. One disadvantage of using pilot symbols to estimate the SIR is that there may be too few pilot symbols for reliable SIR estimation. Increasing the number of pilot symbols would provide more reliable SIR estimation. However, increasing the resources used for transmission of pilot symbols would decrease the resources available for transmission of user data and result in lower system throughput. Also, changing the number of pilot symbols transmitted in a communication system may require standard revisions, which are not desirable.
Demodulated data symbols may be used as additional pilot symbols to improve reliability of SIR estimation. For example, hard symbol decisions output by a demodulator can be compared with the actual transmitted symbols to generate SIR estimates. Alternatively, soft symbol estimates from a demodulator can be decoded and the decoded data can be used to regenerate an estimate of the transmitted symbols.
There are drawbacks to the use of demodulated data symbols for channel estimation. The use of hard symbol decisions by the demodulator as pilot symbols can cause significant performance problems. It is likely that many of the symbol decisions made of the demodulator in the absence of decoding will be incorrect. As a result, SIR estimation methods based on incorrect symbol decisions will not give an accurate SIR estimate. The use of regenerated data symbols based on the decoder output causes delay in the estimation of the SIR. Additionally, the regeneration of data symbols may require extra hardware and more increased power consumption. These limitations make the regeneration approach costly or infeasible in practice.